Field sprayers and distribution devices or spray booms hitched to work machines, such as tractors, in some cases have very large working widths of 20 meters and more. Such wide spray booms are folded in for transport purposes. In the field, symmetrical cantilevered arms of several meters length are located on both sides of the work machine, which cantilevered arms have a varying spacing from the ground according to surface conditions and field relief. Since the downward-directed nozzles for spreading the spraying agent, which nozzles are arranged on the cantilevered arms, each have a defined spray cone, varying the spacing of the nozzles to the ground results in an uneven covering of the field with spraying agent. In addition, the danger of the spraying agent drifting greatly increases with the spacing of the spray nozzles from the ground increasing, since even slight air movements negatively affect the targeted distribution of finely dispersed drops. With increasing cantilever dimensions and the associated working width, there is therefore a necessity to guide the spray boom at as uniform a spacing from the ground as possible, and also to have the spray boom follow the ground relief or a ground contour, respectively, since already minimal inclines of the spray boom lead to large spacing differences of the nozzles to the ground.
A method for motion control or regulation of a spray boom is already known from the prior art. EP 2 591 657 A1, for instance, describes a mobile device for spreading liquid and/or solid active agents, the device comprising a spreading boom, which consists of a middle part and lateral cantilevered arms and which is pivotably mounted at a suspension point. For motion control, the middle part is coupled with a frame section of the vehicle via at least one controllable actuating apparatus. The actuating apparatus produces a largely actuating power-free mechanical connection in a first operating mode, in which the spreading boom is to the greatest extent possible decoupled from torques about the pivot axis through the suspension point, which torques result from vehicle movements about the longitudinal vehicle axis. In a second operating mode or in an adjustment mode, respectively, the actuating apparatus additionally induces a defined actuating power or a defined actuating torque between the middle part and the frame section for the purpose of pivoting the spreading boom relative to the frame. This is carried out largely independently of disturbance torques resulting from vehicle movements.
Guiding the spray boom primarily parallel to a ground surface can indeed be realized by means of the above-described system. However, there is no method disclosed that would enable an adaptation of, for instance, only one side or one cantilevered arm of the spray boom.
Furthermore, EP 2 186 405 A1 describes a spray boom and a method for controlling it, by means of which it is intended to approximately enable an adaptation of the spray boom to a ground relief or to a ground contour. The spray boom has at least two cantilevers arranged via two joints at a middle part, with these cantilevers being in turn arranged to be pivotable in relation to one another via horizontal axles, and with the cantilevers being connected by means of joints, and with a setting movement of the cantilevers in relation to one another being actively controllable. The setting movement is carried out by means of an actuator, where the actuator can in turn be designed as a hydraulically operating cylinder.
The problem arising with such spray booms, in which the cantilevers can be pivoted about horizontal axles by means of hydraulic cylinders, is that the cantilevers do not always move symmetrically to each other. If, for instance, both cantilevers are pivoted, they do not move evenly in relation to each other due to the uneven movements of the cylinders assigned to the respective cantilevers, and this in turn causes a torque to act on the boom suspension, which torque needs to be absorbed and which also negatively affects the distribution of the spray liquid. Although various attempted solutions are known for this case, for example by controlling the cylinders by means of flow divider valves, these various attempts are also subject to construction-related inaccuracies, so that it cannot be ensured that the cantilevers move symmetrically to each other.
Beyond that, FR 2 965 454 A1 discloses a spray boom with two pivotably movable cantilevered arms, of which the positions are detected. The cantilevered arms are guided in a position-controlled manner by the relative positions of the pivotably movable cantilevered arms to the ground surface being respectively detected and a realignment of the at least two cantilevered arms being carried out in the context of an autonomous regulation based on the detected relative positions resulting from a pivoting motion in relation to the ground surface. A further regulation parameter can override the alignment such that one of the arms can optionally be pivoted more strongly than is specified by the autonomous regulation.
FR 2 690 811 A1 finally discloses a spray boom control in which it is possible to switch between an automatic regulation and a manually superimposable position control, where the manually set position is first maintained for a definable period of time until the automatic regulation sets in.